Interesting question re: APC & T cell

Mark Kaplan mkaplan at
Sat Sep 2 11:23:49 EST 1995

In article <1995Sep1.212404.1 at>,
mdcabl at wrote:
> I had this question come up in journal club and didn't have clue how to answer
> it. I can't find anything in medline but that doesn't mean much.  The question
> was: after TCR engagement of the MHC/peptide, how do the APC and T cell
let go?
   Since TCR/MHC interactions are a dynamic process with hundreds of TCRs
interacting with hundreds of MHC-peptide complexes the binding of the two
cells is a cumulitive result of all individual reaction.  It was my
impression that TCR surface expression was somewhat downregualted
following activation thus decreasing the avidity so that the cells fall
off each other.  In any cases I don't think the interaction is so tight
that the cells are stuck.  It's simply a matter if the cells stay together
long enough to activate.

> And, which cell "gets" the peptide.  It was speculated that either the TCR or
> MHC gets cleaved, maybe both... In which case, the molecules might become
> soluble?  Anybody have an idea or want to speculate?
   MHC binds the peptide and would keep it.  TCRs have very low affinity
for free peptide.

> Cheers,
> Allen Black
> Dept. of Pathology
> Univ. of Newcastle

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